By new activation methods, namely, activation by Cs, Sb, and O2(our former new method), or Cs, Ag, and O2(our present new method), stabilized negative electron affinity (NEA) cold cathodes can be obtained, and continuous operation over 6000 h has been achieved with GaP‐GaAlP cold cathodes at emission current density of about 10−1A/cm2. It is found that a major source of rapid degradation of the cold cathode is the loss of the activation material from NEA surface because of nonthermal equilibrium for the activation material. By the new activation methods, the efficiency of the cold cathode showed an increase of 20 ∼60% over that of the conventional method.